The definition of Gibbous as pertaining to the Moon or planets is:
More than half but less than fully illuminated.
This applies to the image above. The full Moon appears very flat when viewed through telescopes. The full illumination of the moon by the Sun produces very few shadows and therefore the features, such as craters or mountains, do not stand out in relief. Phases of less than full reveal more of the Moon's surface features. Possibly the most pleasing images of the Moon are viewed during the first or last quarter phase.